FIGS. 7 through 9 illustrate prior art systems. Referring to FIGS. 7 and 8, a chain drive system for driving auxiliaries for use in transmitting rotation from a crank shaft of an engine to a cam shaft or the like has a chain c wrapped round a sprocket a on the driving side and a sprocket b on the driven side as shown in FIG. 7 and a shoe tensioner lever d has a shoe e to engage the outside face of the slack run of the chain c.
The tensioner lever d has a pivotal support end f with a pivot guide portion therein with a bearing hole k to be fitted over a larger-diametered portion j of a stepped bolt i threaded in a tapped hole h in a fixed part g on the engine side as shown in FIG. 8.
The axial length of the larger-diametered portion j is somewhat larger than the thickness of the pivot guide portion f of the tensioner lever d. The tensioner lever d, in the state where the stepped bolt i is secured to the fixed part g, is allowed to oscillate with the stepped bolt i taken as the axis of oscillation, while it is restricted in its axial movements between the head of the stepped bolt and the fixed part g.
Further, as shown in FIG. 7, the rear side of the other end portion of the tensioner lever d is pushed and urged by a push plunger m of a tensioner l in the direction to the outside of the chain c, so that a suitable tension is provided to the chain c through the shoe e to prevent it from slackening to thereby prevent the chain c from vibrating while in motion.
FIG. 9 shows an example of another pivotal support structure of the prior art for pivotally supporting a tensioner lever on a fixed part on the engine side. In the pivotal support structure of FIG. 9, a collar n is interposed between the bearing hole k' in the pivot guide portion f of the tensioner lever d' and the bolt i'. The axial length of the collar n is made somewhat larger than the thickness of the pivot guide portion f' and, when the collar n is fixedly secured as shown in FIG. 9 by screwing the bolt i' into the tapped hole h' in the fixed part g' on the engine side, the tensioner arm d' supported with the bearing hole k' in the pivot guide portion f' fitted over the peripheral face of the collar n is allowed to oscillate with the bolt i' taken as the shaft of oscillation.
With the design using a stepped bolt as shown in the above described FIG. 8, there have been problems, e.g., the stepped bolts are expensive because they are bolts of special form, difficult to be standardized as engine parts, and involve difficulties in management of parts.
In the design shown in FIG. 9, the bolts themselves and the cylindrical collars are not expensive because standardized bolts can be used. However, when attaching the tensioner lever to the engine, there have been problems, e.g., three parts, i.e., the tensioner lever, the collar, and the bolt, must be attached as one set of parts and the work to insert the collar into the bearing hole in the pivot guide portion of the tensioner lever and screw the bolt into the tapped hole in the fixed part of the engine has been difficult for the worker to perform even when both hands are used.